(1) Field of the Invention
This invention relates to pipes and more particularly to plastic protectors for the threaded end of pipe.
(2) Description of the Prior Art
Tubular goods, such as oil field production pipe, is very expensive and is handled in large quantities. One oil well may require more than four hundred joints of thirty foot pipe. The joints usually are stored out of doors where they are subjected to the deleterious effects of the atmosphere. The threaded ends of a pipe are especially susceptible to oxidation and must be suitably protected.
In handling pipe joints, it is customary to place protectors onto the threaded marginal ends thereof, with one protector being utilized on the pin end and another different size protector being employed on the box end of the pipe.
The protectors usually are screwed into threaded relationship respective to the threaded marginal ends of the pipe, and sometime changes in climatic conditions causes the protectors to become firmly engaged with the pipe threads so that it is very difficult to subsequently remove the protector from the end of the pipe. At other times temperature changes cause the protectos to loosen so that it easily becomes disengaged from the end of the pipe. Moreover, many protectors are provided with an irregular outer surface area so that as one pipe joint makes rolling contact with another, the protectors will inadvertently be unscrewed from the pipe.
There are two main problems with plastic protectors for pipe, particularly oil field pipe. One, the difference in temperature expansion between plastic and steel, and two, the rough handling.
The plastic has thermal expansion which greatly exceeds that of steel. Furthermore, the plastic when warm is soft and more deformable wherein at cold temperatures it is less deformable and more brittle.
The plastic thread protectors may be applied either in hot or cold climates. If they are applied in hot climates, they will contract in cold climates which may cause the protectors to crack and break. If they are applied in cold climates when they warm up and expand if they are on the outside of the threads they may expand to an extent that they are loose.
It will be understood that the temperatures can be extreme, they range all the way from the tropics and desert climates where the pipe sitting in the sun reaches extremely high temperatures or it may be in the artic wherein the pipe goes to extrememly cold temperatures. In the sunshine with the sun shining on the pipe, the pipe can often reach temperatures above 160.degree. F. (72.degree. C.) while in the artic the pipe temperature can be below -60.degree. F. (-50.degree. C.).
Due to the rough handling of the pipe, the external thread protector can be impacted which may either cause cracking of the thread protector if it is cold and brittle; when it will also have greater tensile stresses upon it. If the protector ever cracks it will be loose and will be susceptible to coming off in the event of further vibrations. If the temperature is warm, the rough handling will cause greater deformation of the threads into the thread protector. This impact upon the thread protector will cause the threads to make greater indentations into the thread protector, which further vibrations or rough handling can cause it to come loose.
Joints of pipe are available in many different diameters and it is, therefore, necessary for the manufacturer of the thread protector to supply two different size protectors (internal and external) for each size of pipe. This represents a large capital investment in manufacturing facilities and stock.
Accordingly, it is desirable to be able to reduce the number of protectors required for a finite number of pipe joints. Furthermore, it is desirable to provide a protector which does not loosen nor tighten an appreciable amount during ambient changes in temperature. Moreover, it is desirable to provide a protector which is low in cost, easily installed and removed from the threaded ends of the pipe, and which does not inadvertently become unscrewed during the handling of the pipe. Such a protector is the subject of this invention.
Also in many cases where the pipe is coated internally, it is desired to seal the ends of the pipe to protect the coating and not leave it exposed.
In the parent application, the Examiner considered the following patents to be pertinent:
Gray, Jr., U.S. Pat. No. 3,104,681 PA0 Ferguson, U.S. Pat. No. 2,551,834 PA0 Pfeil et al., U.S. Pat. No. 2,632,479
GRAY JR. disclose a plastic closure for protecting pipe threads. It discloses a tapered plug. The thread engaging portions of it are smooth, both internally and externally.
FERGUSON discloses a protective plastic cap made of vinylite, cellulose acetate, cellulose acetate butyrate or the like. If is disclosed for use with machine type threads, i.e., non-tapered threads. The entire description of the gripping action is by the deformation of the threads into the ribs.
PFEIL ET AL. discloses a thread protector which has ribs or protuberances 12 of perferable triangular shape which are softer than the threads to be protected.